One of the major drawbacks for restorative dentistry is the polymerization shrinkage and the consequential shrinkage stress in methacrylate-based dental composites. An efficient way to reduce shrinkage stress is the incorporation of addition fragmentation chain transfer agents (AFCT agents). In this contribution, five novel polymerizable allyl sulfones were synthesized in four to five steps. A photo-DSC study was carried out in order to evaluate the influence of the addition of each AFCT agent on the polymerization rate of a dimethacrylate-based monomer mixture. The glass transition temperature (Tg) of the resulting networks was measured using DMTA. Dental composites based on these new chain transfer agents (CTAs) were prepared. A combination of camphorquinone, ethyl 4-(dimethylamino)benzoate and bis-(4-t-butylphenyl)-iodonium hexafluorophosphate was selected as photoinitiator system. Low shrinkage force values, suitable ambient light working time and excellent mechanical properties were obtained for all CTA based materials. Composites based on three of the synthesized CTAs even exhibited higher flexural modulus than the corresponding CTA-free material. Furthermore, a significant reduction of unreacted CTA leaching was found if a polymerizable moiety was introduced in the CTA structure. Hence, the incorporation of polymerizable allyl sulfones in dental composites is a promising strategy to obtain low shrinkage materials exhibiting improved biocompatibility.

Objectives. To evaluate high refractive index methacrylates as diluents for the formulation of radiopaque esthetic bulk-fill composites. Methods. 2-(4-Cumylphenoxy)ethyl methacrylate 1, 2-(2-phenylphenoxy)ethyl methacrylate 2 and 2-[2-(2-phenylphenoxy)ethoxy]ethyl methacrylate 3 were synthesized and characterized by H-1 NMR spectroscopy. The reactivity of each monomer was studied using photo-DSC. Bulk-fill composites based on monomers 1-3 were formulated. Translucency (before and after light cure) was measured using a spectrophotometer. The depth of cure and the water sorption of these materials were determined according to ISO 4049. The flexural strength and modulus of elasticity were measured using a three-point bending setup, according to ISO 4049. The shrinkage force was assessed based on a method described by Watts et al. using a universal testing machine. Results. Monomers 1-3 were easily synthesized in two steps. They exhibit a low viscosity and a high refractive index (1.553-1.573). Monofunctional methacrylates 1-3 were found to be more reactive than triethylene glycol dimethacrylate (TEGDMA). Bulk-fill composites based on these monomers were successfully prepared. They exhibit a high depth of cure and excellent esthetic properties (low transparency). These composites provide higher flexural modulus as well as lower water sorption than a corresponding material based on TEGDMA. Methacrylates 1 and 3 are particularly interesting as they led to composites showing lower shrinkage force. Significance. Methacrylates 1-3 are promising diluents for the formulation of highly esthetic radiopaque bulk-fill composites. (c) 2020 Published by Elsevier Inc. on behalf of The Academy of Dental Materials.

Objective. The objective of this work is to find potential alternative monomers to 2-hydroxyethyl methacrylate (HEMA) for dental materials (self-etch adhesives and luting composites).Methods. Monomers 19 were tested as potential HEMA substitutes. Methacrylates 4, 5 and 6 and (N-methyl)acrylamides 79 were synthesized and characterized by 1H NMR spectroscopy. The reactivity of each monomer was studied using photo-DSC. Mixtures of monomers 19 with the urethane dimethacrylate UDMA (1/1: wt/wt) were formulated and cured. The water sorption and solubility of these materials were determined according to ISO 4049. Luting composites based on monomers 19 or on HEMA were formulated. The flexural strength and modulus of elasticity were measured using a three-point bending setup, according to ISO 4049. Self-etch adhesives containing monomers 19 or HEMA were prepared and used to mediate a bond between the dental composite Tetric EvoCeram and both dentin and enamel. The shear bond strength (SBS) was measured using a Zwick universal testing machine.Results. Polymerizable diols 3 and 4 as well as (N-methyl)acrylamides 79 were found to be significantly more reactive than HEMA. Resins based on the hydrophilic monomers 3, 7 and 8 exhibited a significantly higher water sorption than the corresponding HEMA-containing material. Luting composites containing monomers 2, 3, 6 and 7 showed similar or even improved mechanical properties compared to the reference material containing HEMA. Self-etch adhesives containing monomers 4 and 9 provided significantly higher dentin SBS than the reference material.Significance. Some of the evaluated monomers are promising candidates for the development of HEMA-free dental materials. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Five new urethane groups containing monomers 1 – 5 , acetylated glycerol dimethacrylate (AGDMA), and glycerol trimethacrylate (GTMA) are synthesized as alternative diluents to triethylene glycol dimethacrylate (TEGDMA) for dental resins or composites. The synthesized monomers are characterized by means of 1 H NMR, 13 C NMR, and IR spectroscopy. The secondary acrylamide group containing hybrid monomers 1 and 2 are solids. However, the monomers 3 – 5 , AGDMA and GTMA are colorless and relatively low-viscosity liquids. They are not mutagenic in the Ames test and show a lower cytotoxicity and a lower polymerization shrinkage compared to TEGDMA. The tertiary amide group containing crosslinker 3 shows a significantly higher photopolymerization rate compared to that of TEGDMA in the presence of the monomolecular Ge-based photoinitiator Ivocerin. The synthesized diluents are evaluated in experimental dental formulations for resins, cements, and direct filling composites using a conventional binary camphorquinone/amine photoinitiator.

The 2-ethoxycarbonylallyl 5-(1,2-dithiolane-3-yl)-pentanoate monomer (AODS) includes in its molecular structure CC and SS reactive bonds allowing it to behave as a bi-functional monomer, possessing two groups, however, with different reactivity for use in polymer chain building. The polymerization-specific features of this monomer are the absence of auto-acceleration and polymer chain crosslinking. Polymerization proceeds readily through most free-radical initiators. One exception, carboxy-peroxides are rapidly decomposed without the production of free radicals. AODS is partially converted to a gel without the consumption of double bonds during monomer dissolution in certain organic solvents and after being mixed in solution with carboxy-peroxides. The determined AODS-co-MMA copolymerization parameters are r(1)=2.61, r(2)=0.23 if Luperco peroxide is used as a polymerization initiator, and r(1)=2.71, r(2)=0.38 if AIBN is used.

5-Methacrylamidopentyl (3a), 10-(N-methylacrylamido)decyl (3b), or 11-(N-methylacrylamido)undecyl dihydrogen phosphate (3c) are synthesized by (meth)acrylation of the corresponding -aminoalkane-1-ols with methacrylic anhydrid or acryloyl chloride followed by phosphorylation of the formed -(meth)acrylamidoalkane-1-ols. The monomers show a significantly improved hydrolytic stability compared to the corresponding methacrylate-based dihydrogen phosphates. The photopolymerization of 3ac with a bis(acrylamide) crosslinker confirms a high reactivity in the free-radical copolymerization. These monomers enable the mediation of a strong bond between the enamel or dentin surface and a restorative composite under self-etching conditions.

p-tert-Butylcalix[6]arene was acylated with different carboxylic acid anhydrides to improve their solubility in dimethacrylate cross-linkers. An esterification of p-tert-butylcalix[6]arene 1 with octanoic anhydride followed by methacrylation of the residual hydroxy groups with methacrylic anhydride resulted mainly in the formation of a pentaoctanoatemonomethacrylate 2a. In the radical polymerization of methyl methacrylate the inhibition effect of residual hydroxy groups in 2a was evaluated. Dimethacrylate containing composites based on a monomer matrix of cross-linking dimethacrylates and 0-30 wt.% of 2a were prepared. The addition of 2a resulted in a significant decrease of the polymerization shrinkage, whereas the modulus of elasticity of the visible light cured composites was not affected.

Because of the poor solubility of the commercially available bisacylphosphine oxides in dental acidic aqueous primer formulations, bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide (WBAPO) was synthesized starting from 3-(chloromethyl)-2,4,6-trimethylbenzoic acid by the dichlorophosphine route. The substituent was introduced by etherification with 2-(allyloxy)ethanol. In the second step, 3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoic acid was chlorinated. The formed acid chloride showed an unexpected low thermal stability. Its thermal rearrangement at 180 °C resulted in a fast formation of 3-(chloromethyl)-2,4,6-trimethylbenzoic acid 2-(allyloxy)ethyl ester. In the third step, the acid chloride was reacted with phenylphosphine dilithium with the formation of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine, which was oxidized to WBAPO. The structure of WBAPO was confirmed by 1H NMR, 13C NMR, 31P NMR, and IR spectroscopy, as well as elemental analysis. WBAPO, a yellow liquid, possesses improved solubility in polar solvents and shows UV–vis absorption, and a high photoreactivity comparable with the commercially available bisacylphosphine oxides. A sufficient storage stability was found in dental acidic aqueous primer formulations.

Objectives. The objective of this study was to investigate the use of a new, partially aromatic urethane dimethacrylate in visible-light cured resin-based composite restoratives. Selected mechanical properties, such as flexural strength and flexural modulus of elasticity, of model monomer mixtures and composites containing the new urethane dimethacrylate were investigated and compared to the properties of materials that are based on Bis-GMA, at present the most frequently used cross-linker in restorative composites. In addition, the polymerization shrinkage and the water sorption of selected composites were determined.Methods. The flexural strength, flexural modulus of elasticity, and the water sorption were determined according to ISO 4049:2000. Test specimens (rods: 2 mm x 2 mm x 25 mm; discs: d = 15 mm and h = 1 mm) of the investigated composites were prepared in stainless steel molds and light-cured (150 mW/cm(2), 2 x 180 s). The flexural strength and flexural modulus of rods were measured after the samples had been stored under dry conditions or in water for 24 h at 37 degrees C as well as after they had been stored in water for 7 days at 37 degrees C. The water sorption was determined with discs. The polymerization shrinkage was calculated from the densities of the uncured composite pastes and cured composites.Results. Visible light cured mixtures of dimethacrylate diluents with the new urethane dimethacrylate and composites based on these mixtures show a reactivity, flexural strength, flexural modulus of elasticity, polymerization shrinkage and water sorption similar to those of materials that are based on Bis-GMA. The composites did not show any strong deterioration of the mechanical properties after water storage. (C) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

2-Vinylcyclopropane-1-phosphonic acid diesters 1a - d were synthesized by the reaction of trans-1,4-dibromo-2-butene with alpha-substituted phosphonic acid diesters. Esterification of 1-ethoxycarbonyl-2-vinylcyclopropane-1-carboxylic acid with dimethyl 2-hydroxyethyl-phosphonate gave the 2-vinylcyclopropane phosphonic acid dimethylester 1e. The silylation of phosphonic acid diesters 1a - e by halotrimethylsilanes followed by solvolysis with methanol or water resulted in the formation of phosphonic acids 2a - e. In the case of steric hinderance of the phosphoryl group, monoesters 3c, d were also formed. Furthermore, ethyl carboxylate 1b could be chemoselectively cleaved by aqueous potassium hydroxide to carboxylic acid 4.

Objectives. The objective of this study was to investigate the use of three new bis(acrylamide)s as cross-linker in resin-based composite restoratives. Selected mechanical properties such as flexural strength and flexural modulus of model composites containing bis-(acrylamide)s were investigated and compared to the properties of composites that are based on only conventional dimethacrylates. In addition, the hydrolytic stability of composites containing an acidic monomer was examined.Methods. The flexural strength and flexural modulus of elasticity were determined according to ISO 4049:2000. For this purpose, test specimens (2 mm x 2 mm x 25 mm) of the composites investigated were prepared in stainless steel moulds and light-cured (150 mW/cm(2), 2 x 180 s). The flexural strength and flexural modulus were measured after the samples had been stored in dry conditions or in water for 24h at 37 degrees C as well as after they had been stored in water for 7 days at 37 degrees C, and in certain cases, after they had been boiled for 24 h in water.Results. Visible light cured mixtures of dimethacrylates with bis-(acrylamide)s and composites based on these mixtures show a similar reactivity, flexural strength and flexural modulus of elasticity compared to materials that contain only dimethacrylate. The composites did not show any deterioration of the mechanical properties after water storage. Only when strongly acidic monomers were added to the composites containing dimethacrylates or bis(acrylamide)s did the flexural strength and flexural modulus of the samples decrease after they were stored in water.Significance. Bis-(acrylamide)s were similarly reactive than dimethacrylates and therefore can be used as diluents to substitute dimethacrylate diluents in composites. Although the bis-(acrylamide)s are entirely soluble in water, non-ionic materials based on bis(acrylamide)s did not strongly change their mechanical properties during storage in water. (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.